Glucose tolerance test with a single abnormal value as a predictor of type 2 diabetes mellitus: a multicenter retrospective study

Clinical implication of a single abnormal value (SAV) in the 100 g oral glucose tolerance test during pregnancy has not been established. We aimed to evaluate the risk of postpartum type 2 diabetes mellitus (T2DM) and investigate adverse pregnancy outcomes in women with SAV, using a retrospective database, from seven medical centers of Korea. Based on the Carpenter-Coustan criteria using two-step approach, pregnancy and postpartum outcomes were compared, among normoglycemic, SAV, and gestational diabetes mellitus (GDM) groups. Among 9353 women, 342 (3.66%) and 418(4.47%) women were included in SAV and GDM groups, respectively. SAV and GDM groups showed significantly higher rates of postpartum T2DM than normoglycemic group (7.60%, 14.83%, and 1.82%, respectively, p < 0.001). And SAV group showed significantly higher rates of pregnancy associated hypertension, preterm birth, and neonatal hypoglycemia and sepsis, compared to normoglycemic group (neonatal sepsis, p = 0.008; the others, p < 0.001). In multivariate analysis, postpartum T2DM was associated with SAV, GDM (with/without insulin), nulliparity, pre-pregnancy BMI, chronic hypertension, hyperlipidemia, and DM family history. A scoring model to predict postpartum T2DM within 5 years, achieved an area under the curve of 0.74. This study demonstrated that not only GDM, but also SAV is a significant risk factor for postpartum T2DM.


Eligibility criteria and group definition
This study included data from women who delivered between January 2009 and December 2020 at seven hospitals of the Catholic University of Korea College of Medicine.We used a two-step approach to diagnose GDM between 24 + 0 and 28 + 6 weeks of gestation.Those with an abnormal value (≥ 140 [mg/dL]) in 50 g GCT were referred to undergo 100 g OGTT.The normal cutoff value of the OGTT followed Carpenter and Coustan criteria (fasting blood glucose, 1-h, 2-h, and 3-h post-glucose loading of < 95 [mg/dL], < 180 [mg/dL], < 155 [mg/dL], and < 140 [mg/dL], respectively) 1 .
We included singleton pregnancies with all medical records for GDM screening and diagnostic tests.Patients with pre-gestational diabetes, fetal anomalies, and multifetal pregnancies were excluded.Additionally, we excluded patients with a positive 50 g GCT but below the cut-off value in all criteria of the subsequent 100 g OGTT (Fig. 1).
Preterm delivery was defined as delivery at less than 37 weeks of gestation.PAH included pre-eclampsia, superimposed pre-eclampsia, pregnancy-induced hypertension (PIH), and eclampsia.Postpartum bleeding was defined as cumulative blood loss of > 1000 mL or blood loss accompanied by signs and symptoms of hypovolemia 14 .Excessive weight gain refers to Institute of Medicine Weight Gain Recommendation for pregnancy 15 .The diagnosis of postpartum diabetes was based on the occurrence of ICD code E10-14.Additionally, we include the cases of HbA1c ≥ 6.5% or fasting blood sugar (FBS) ≥ 126 mg/dL or plasma glucose concentration ≥ 200 for 2 h after a 75 g OGTT within 5 years of delivery.The Korean Diabetes Association recommends that women with a history of gestational diabetes receive an oral glucose tolerance test 4 to 12 weeks after delivery 16 .Afterwards, these women were recommended to get screening tests for type 2 DM every year for the rest of your life, including HbA1c or FBS or OGTT.Chorioamnionitis was defined based on International Classification of Disease (ICD) code O411 or suspicious findings such as intrapartum fever, maternal leukocytosis, purulent cervical discharge, and fetal tachycardia 17 .Polyhydramnios was defined based on ICD code O40 or sonographic values exceeding an amniotic fluid index of 24 cm or a single deep pocket of 8 cm 18 .LGA was defined as cases with ICD code P08 or specified as LGA in the medical record refers to birth weight above the 90 th percentile for gestational age 19 .Neonatal hypoglycemia was defined based on ICD code P70 or E16 or blood sugar level < 40 mg/ dL during the first 4 h of life or < 45 mg/dL during the first 4 to 24 h of life following the American academy of Pediatrics (AAP) guidelines 20 .We defined a composite neonatal outcome as one or more NICU admissions, RDS, TTN, mechanical ventilation, HIE, IVH, jaundice, hypoglycemia, and sepsis.
Furthermore, the women involved in this study were redistributed into two groups: (1) undiagnosed with diabetes within 5 years after delivery (control group), and (2) diagnosed with diabetes within 5 years after delivery (postpartum T2DM group).
Possible risk factors for postpartum T2DM were analyzed using univariate and multivariate regression analyses.For a more accurate analysis, GDM was divided into with or without insulin treatment during pregnancy.

Statistical analysis
Baseline characteristics and pregnancy outcomes were compared between the groups using the chi-square or Fisher's exact tests for categorical variables and t-tests for continuous variables.We conducted a post-hoc analysis using the Bonferroni method for multiple subgroup comparisons.The significance level for all statistical tests was set at p < 0.05.Variables with statistical significance in the univariate analysis were subjected to multivariate stepwise logistic regression.A scoring model for estimating the risk of T2DM within 5 years of delivery was developed using independent associated factors in the multivariate analysis.Receiver operating characteristic (ROC) analysis was performed to determine the screening performance.A Kaplan Meier Curve to make the time dynamics of postpartum T2DM occurrence was also analyzed.All analyses were performed using the Statistical Analysis Software (version 9.4; SAS Institute, Inc., Cary, NC, USA).Assistance with statistical analysis was provided by biostatisticians (YounJu Lee and Minjoo Lee) employed by contract research organization, Medical Excellence Inc., Seoul, Republic of Korea.

Baseline characteristics according to GDM screening results
This study initially included 35,098 patient deliveries between 2009 and 2020 at the seven university hospitals.After applying the exclusion criteria, 9,353 cases were included in the study (Fig. 1).Of these, 8,593 (91.87%) cases were in the normoglycemic group, and 342 (3.66%) and 418 (4.47%) cases were in the SAV and GDM groups, respectively.
The baseline characteristics of the participants are shown in Table 1.Compared with the normoglycemic group, the SAV and GDM groups showed significantly older maternal age and higher BMI (p < 0.001).Pregnancy by IVF, the percentage of women with BMI ≥ 25 kg/m 2 before pregnancy, BMI ≥ 30 kg/m 2 at delivery, and chronic hypertension were also significantly higher in the SAV and GDM groups than in the normoglycemic group (p < 0.001).But weight gain (kg) during pregnancy was significantly higher in normoglycemic group than SAV and GDM groups (p < 0.001).In parous women, previous GDM history was significantly higher in the SAV and GDM groups than in the normoglycemic group (p < 0.001); however, previous histories of PAH and macrosomia were significantly higher in the GDM group than in the normoglycemic group but not in the SAV group (previous history of PAH: normoglycemic vs. GDM, p < 0.001, normoglycemic vs. SAV, p = 0.184; previous macrosomia: normoglycemic vs. GDM, p = 0.031, normoglycemic vs. SAV, p = 1.0).There was a significant difference in family history of DM and 50 g GCT results among the three groups (p < 0.001).

Pregnancy outcomes according to GDM screening results
The data on adverse pregnancy and neonatal outcomes are presented in Table 2. Compared with the Table 1.Baseline characteristics of patients.Values are expressed as means (standard deviation, SD), or n (%).SAV single abnormal value in 100 g OGTT, OGTT oral glucose tolerance test, GDM gestational diabetes mellitus, IVF in vitro fertilization, BMI body mass index, CKD chronic kidney disease, PCO polycystic ovarian syndrome, SLE systemic lupus erythematosus, PAH pregnancy-associated hypertension, DM diabetes mellitus, GCT glucose challenge test, OGTT oral glucose tolerance test.*p-value: normoglycemic vs SAV vs GDM.# Post-hoc p-value using Bonferroni methods: normoglycemic vs SAV.$ Post-hoc p-value using Bonferroni methods: normoglycemic vs GDM.† PAH: corresponding to one of preeclampsia, superimposed preeclampsia, pregnancy-induced hypertension, and eclampsia.† † macrosomia: corresponding to baby birth w eight above 4 kg.† † † Excessive weight gain: refers to Institute of Medicine Weight Gain Recommendation for pregnancy.www.nature.com/scientificreports/normoglycemic group, the SAV and GDM groups showed significantly higher rates of preterm birth, PAH, neonatal hypoglycemia, and NICU admissions (preterm birth, p < 0001; PAH, p < 0.001; neonatal hypoglycemia, p < 0.001; NICU admissions, p = 0.023).There were significantly higher rates of RDS, use of surfactants, jaundice, and neonatal composite outcomes in the GDM group than in the normoglycemic group (RDS, p = 0.01; use of surfactant, p = 0.003; jaundice, p = 0.001; neonatal composite outcome, p = 0.004).However, there was a significantly higher rate of sepsis in the SAV group than in the normoglycemic group, but not in the GDM group (normoglycemic vs. SAV, p = 0.007; normoglycemic vs. GDM, p = 1.0).Regarding postpartum prognosis, there was a significant difference among the three groups in the diagnosis of T2DM within 6 months and 5 years after delivery (p < 0.001).In the post hoc test, the diagnosis of diabetes within 6 months after delivery significantly differed between the normoglycemic and GDM groups (normoglycemic vs. GDM, p < 0.001; normoglycemic vs. SAV, p = 1.0).Additionally, the diagnosis of diabetes within 5 years after delivery showed significant differences among the three groups (p < 0.001).

Maternal characteristics according to the diagnosis of T2DM within 5 years after delivery
When the postpartum T2DM group was compared with the control group, women in the postpartum T2DM group had a significantly higher rate of SAV and GDM (with or without insulin treatment) following GCT were significantly higher in the postpartum T2DM group than in the control group (p < 0.001) (Table 3).Women in the postpartum T2DM group also had significantly higher rates of nulliparity, obesity, chronic hypertension, PCO, hyperlipidemia, hypothyroidism, previous GDM history, previous preeclampsia history, PAH in the current pregnancy, and family history of DM, compared to women in the control group.But mean weight gain during pregnancy was significantly higher in control group than postpartum T2DM group (p < 0.001) and there was no significant difference in the proportion of women with excessive weight gain between control and postpartum T2DM groups.In the univariate analysis, ORs of SAV, GDM (with or without insulin treatment), nulliparity, BMI before pregnancy ≥ 25 kg/m 2 , < 30 kg/m 2 , BMI before pregnancy ≥ 30 kg/m 2 , BMI at delivery ≥ 30 kg/m 2 , chronic hypertension, PCO, hyperlipidemia, hypothyroidism, previous GDM history, previous PAH history, family history of DM and pregnancy complication of PAH were significantly increased in the postpartum T2DM group (Table 4).
Stepwise multivariate logistic regression analysis was performed using variables that were significantly different between the postpartum T2DM and control groups in the univariate analysis.In the multivariate logistic regression analysis, SAV (odds ratio  4).Kaplan-Meier curves showed that cumulative incidence of T2DM diagnosis within 5 years after birth was significantly higher in the GDM and SAV group as presented in Fig. 2.

Stratified risk score for predicting Postpartum T2DM
We developed a statistical scoring model using independent risk factors to estimate the individual risks of postpartum T2DM (Table 5).In ROC analysis, the scoring model achieved an area under the ROC curve (AUC) of 0.746 (Fig. 3).

Principal findings
This study demonstrated that SAV was a significant risk factor for postpartum T2DM.In addition, the Kaplan Meier curve showed similar occurrence of T2DM between SAV and GDM without insulin groups, within 5 years after birth.Women with SAV had clinical characteristics similar to those with GDM, including older maternal age, higher BMI, conception by IVF, chronic hypertension, previous GDM history, and family history of DM.We also found a higher incidence of adverse pregnancy outcomes, including preterm birth, neonatal hypoglycemia, neonatal sepsis, NICU admissions, and PAH in the SAV group than in the normoglycemic group.However, those who oppose this approach claim that the GDM group with a one-step approach has a 3.4-fold higher risk of T2DM; additionally, children with GDM had a higher risk of obesity than the normoglycemic group when observed for 11 years 27,28 .The American Diabetes Association concluded that GDM diagnosis can be accomplished with either of the two strategies; however, there is still controversy regarding which method is better regarding long-term prognosis 5 .When only SAV is considered in a two-step approach, it is called borderline GDM, impaired glucose tolerance, or mild hyperglycemia [29][30][31] .Previous studies have suggested that SAV and GDM occur via the same mechanism caused by increased insulin resistance during pregnancy [32][33][34][35][36] .A meta-analysis of 25 studies demonstrated that patients with SAV on a 100 g OGTT had increased LGA, neonatal hypoglycemia, and cesarean delivery 37 .A randomized controlled trial reported similar perinatal outcomes in SAV and untreated mild GDM 38 .In prospective study, pregnancy outcomes improved when women with SAV were managed similarly to those with GDM 39 .As a long-term outcome, several studies concluded that SAV diagnosed during pregnancy increases future abnormal glucose tolerance similar to GDM 32,35,40,41 .Moreover, previous study found that SAV is independent risks factor of T2DM after 5 years of delivery 41 .
Our study also demonstrated that not only GDM, but also SAV during pregnancy were significant risk factor for postpartum T2DM.We subdivided the GDM group according to whether or not they were treated with insulin during pregnancy.There was similar risk of postpartum T2DM in SAV group, compared to GDM without insulin treatment.This study suggests postpartum life-style modification in women with SAV, although future studies may be needed whether postpartum monitoring or preventive education in women with SAV is useful for their long-term health.

Strengths and limitations
Our data were obtained from seven centers in different regions of Korea, which have a same diagnostic protocol for GDM.In this study, SAV showed a comparable risk of postpartum T2DM to women with GDM who did not require insulin during pregnancy.Using independent risk factors from this study, we developed a scoring system that can be applied to individual patients.In this study, the average BMI and the proportion of obesity tended to be low.Although the obese population is increasing in Korea, the obesity rate is still lower than in the West.However, it is known that Asian women have moderate risk of GDM, despite having a relatively lower BMI compared to other ethnic groups 42 .Therefore, this study may be more meaningful as a risk model for this population, although future validation studies are required for clinical application, Our study is not free for limitations because of retrospective nature.First, there were missing data for those who did not receive a 75 g OGTT test after delivery.Second, cases with abnormal 50 g GCT but no abnormal OGTT results or 100 g OGTT were excluded.This group was clearly judged to be low risk in the confirmatory test.Therefore, there was no need to compare the risk with the group that was already being managed as a low-risk group because the 50 g test was negative.Previous study comparing between a 50 g negative group and a 50 g positive but negative in all results of 100 g OGTT showed that there was no difference in pregnancy outcomes between the two groups 43 .Lastly, incidence of GDM was relatively low in this study.In Korea, GDM prevalence has been increased from 7.5% in 2009 to 18.2% in by 2021 42 .The low prevalence of GDM in our study was influenced by the inclusion of historical data from 2009.This also has the impact of excluding patients with GDM who have already been diagnosed and transferred from another hospital.To ensure the accuracy of the study, only patients who receive all tests for GDM in our hospitals were included.
To overcome the limitation of retrospective data, the validation cohort is currently being enrolled.We will use these prospective data to demonstrate the clinical significance of SAV and validate our scoring system and apply it to individual patients.

Figure 1 .
Figure 1.Participant flow chart of the total population.DM diabetes mellitus, SAV single abnormal value in 100 g OGTT, OGTT oral glucose tolerance test, GTT glucose tolerance test, GDM gestational diabetes mellitus.

Figure 3 .
Figure 3. Receiver operating characteristic curve of the scoring model for postpartum type 2 diabetes mellitus within 5 years post-delivery.

Table 4 .
Odd ratios for risk factors of postpartum T2DM using univariate and multivariate stepwise logistic regression analysis.CI confidence interval, OR odds ratio, T2DM type 2 diabetes mellitus, SAV single abnormal value in 100 g OGTT, OGTT oral glucose tolerance test, GDM gestational diabetes mellitus, BMI body mass index, PCO polycystic ovarian syndrome, DM diabetes mellitus, PAH pregnancy-associated hypertension, GDM-IT GDM not requiring insulin treatment, GDM + IT GDM requiring insulin treatment.† Excessive weight gain: refers to Institute of Medicine Weight Gain Recommendation for pregnancy.† † PAH: corresponding to one of preeclampsia, superimposed preeclampsia, pregnancy-induced hypertension, and eclampsia.

Table 5 .
Risk scores for predicting postpartum -T2DM within 5 years after birth.BMI body mass index, DM diabetes mellitus, SAV single abnormal value in 100 g OGTT, OGTT oral glucose tolerance test, GDM gestational diabetes mellitus, GDM-IT GDM not requiring insulin treatment, GDM + IT GDM requiring insulin treatment.† Normoglycemic: corresponding to normal 50 g GCT results.